1. Field of the Invention
This invention relates to a battery charger to charge a rechargeable battery (secondary battery) incorporated in portable electronic equipment through a USB (Universal Serial Bus) interface.
2. Description of the Related Art
In recent years, there has been developed a battery charger to charge a rechargeable battery incorporated in a mobile phone, which is usually kept in a waiting state in a power saving mode and put into an operating state when the mobile phone is connected to the battery charger.
Also, a battery charger to charge a rechargeable battery using a power supply of DC 5 V, which is supplied from a power supply terminal Vbus of the USB that is widely adopted as a serial bus for a personal computer, has come to be adopted in order to increase versatility and to reduce a size and a weight of the battery charger.
Japanese Patent Application Publication No. 2007-60778 discloses a battery charger using the Vbus terminal of the USB, which can provide the battery charger with a sufficient charging current regardless of an amount of current consumed by other peripheral equipment connected to the USB interface.
To save power consumption by the battery charger using the Vbus terminal of the USB described above, how to detect whether the portable electronic equipment such as a mobile phone is connected is an issue.
There is conceived a system which judges that the portable electronic equipment is connected to the battery charger when data communication is performed through the USB interface and certain negotiation is successfully established between the battery charger and the portable electronic equipment.
However, there are problems with the system described above, that is, it requires incorporating a large controller provided with functions to interface with the USB and increases complexity of a structure as well as a cost of the system.